1. What are Domain and Domain Name?
With an Internet address or name, a domain or domain name is the location of a website. For example, the domain name “google.com” points to the IP address “216.58.216.164”. Generally, it’s easier to remember a name rather than a long string of numbers. A domain name contains a maximum of sixty three characters, with one character minimum, and is entered after the protocol in the URL (uniform resource locator), as shown in the following example.
2. What is DNS?
The Domain Name System (DNS) is the internet’s directory. People access online information through domain names, like nytimes.com or Espn.com. Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names into IP addresses so browsers can load internet resources.
Every device connected to the internet has a unique IP address that other machines use to find the device. DNS servers eliminate the need for humans to memorize IP addresses such as 192.168.1.1 (in IPv4), or more complex alphanumeric addresses like 2400:cb00:2048:1::c629:d7a2 (in IPv6).
3. How does DNS work?
The process of DNS resolution involves translating a hostname (like www.example.com) into a computer-friendly IP address (like 192.168.1.1). Every device on the internet has an IP address, and that address is needed to locate the appropriate internet device – much like a street address is used to find a specific house. When a user wants to load a webpage, a translation must occur between what a user types into their web browser (example.com) and the machine-friendly address necessary to locate the example.com webpage.
To understand the process behind DNS resolution, it’s important to understand the different hardware components that a DNS query must pass through. For the web browser, the DNS lookup happens “behind the scenes” and does not require interaction from the user’s computer beyond the initial request.
There are 4 DNS servers involved in loading a webpage:
- Recursive DNS servers – The recursive server can be thought of as a librarian who is asked to go find a particular book somewhere in a library. The Recursive DNS server is a server designed to receive queries from client machines through applications such as web browsers. Typically, the resolver is then responsible for making additional requests in order to satisfy the client’s DNS query.
- Root name servers – The root server is the first step in translating (resolving) human-readable host names into IP addresses. It can be thought of like an index in a library that points to different racks of books – typically it serves as a reference to other more specific locations.
- TLD name servers – The top-level domain server (TLD) can be thought of as a specific shelf in the library in which books are stored. This name server is the next step in the search for a specific IP address, and it hosts the last portion of a hostname (In example.com, the TLD server is “com”).
- Authoritative DNS servers – This final name server can be thought of as a dictionary on a shelf of books, in which a specific name can be translated into its definition. The authoritative name server is the last stop in the name server query. If the authoritative name server has access to the requested record, it will return the IP address for the requested hostname back to the DNS Recursor (the librarian) that made the initial request.
What is the difference between an authoritative DNS server and a recursive DNS resolver? Both concepts refer to servers (or groups of servers) that are integral to the DNS infrastructure, but each performs a different role and exists at different points in the path of a DNS query. One way to think about the difference is that the recursive resolver is at the beginning of the DNS query and the authoritative name server is at the end.
4. What are the 8 steps of DNS lookup?
The user types ‘example.com’ into their web browser and the query goes out to the internet and is received by the Recursive DNS Resolver. Next, the resolver queries the Root DNS server (.). Then, the root server responds to the resolver with the address of the Top-Level Domain (TLD) DNS server (like .com or .net), which hosts information for its domains. When searching for example.com, our request is directed to the .com TLD. Next, the resolver makes a request to the .com TLD. Then, the TLD server responds with the IP address of the domain’s name server, example.com. Finally, the Recursive DNS Resolver sends a query to the domain’s name server. The IP address for example.com is then returned to the resolver from the name server. Then, the Recursive DNS Resolver responds to the web browser with the IP address of the domain that was originally requested. Once the 8 steps of DNS lookup have returned the IP address for example.com, the browser can make a request to the website:
The browser makes an HTTP request to the IP address. The server at that IP returns the webpage to be displayed in the browser (step 10). Completion of DNS lookup and website query – 10 steps What is a DNS Resolver? The DNS Resolver is the first stop in the DNS lookup process and it is responsible for dealing with the client application that made the initial request. The resolver starts the chain of queries that ultimately leads to a URL being translated into the necessary IP address.
Note: A DNS lookup that is not cached will typically involve both recursive and iterative queries.
It’s important to distinguish between a recursive DNS query and a recursive DNS resolver. The query refers to the request sent to the DNS resolver to resolve the query. The recursive DNS resolver is the computer that accepts the recursive query and handles the response by making the necessary requests.
What are the types of DNS queries? In the typical DNS lookup process, there are three types of queries that occur. By using a combination of these queries, the process is optimized for DNS resolution that can help reduce travel distance. In an ideal situation, record data stored in cache will be available, allowing the DNS name server to return a non-recursive query.
5. 3 types of DNS queries
- Recursive query – In a recursive query, the DNS client requests that the DNS server (typically the Recursive DNS Resolver) respond to the client with the requested resource record or an error message if the resolver can’t find the record.
- Iterative query – in this case, the DNS client allows the DNS server to return the best possible answer. If the DNS server queried does not match the query name, it will return a reference to a DNS server authoritative at a lower level of the domain namespace. The DNS client then makes a query to the introduced address. This process continues with additional DNS servers in the query chain until an error occurs or a timeout.
- Non-recursive query – typically, this will occur when the DNS client resolver queries the DNS server for a record that it has authority over or the record exists within its cache. Typically, DNS servers will cache DNS records to prevent consumption and additional load on upstream servers.
